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Note on the velocity of gas-reactions

Published online by Cambridge University Press:  24 October 2008

J. A. Christiansen
J. A. Christiansen
Affiliation:
University of Copenhagen
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Extract

In a recent paper, G. N. Lewis and D. F. Smith have discussed the problem of the velocity of chemical reactions, especially that of the only gas-reaction, the decomposition of N2O5, which had then been proved with sufficient accuracy to be kinetic unimolecular, i.e. unimolecular in the purely empiric sense of the word.

Type
Articles
Information
Mathematical Proceedings of the Cambridge Philosophical Society , Volume 23 , Issue 4 , October 1926 , pp. 438 - 449
Copyright
Copyright © Cambridge Philosophical Society 1926

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References

* Journ. Amer. Chem. Soc., 47, p. 1508 (1925).CrossRefGoogle Scholar

† Zeitschr. Physik. Chem. 104, p. 451 (1923).Google Scholar Attention should especially be called to the remarkable papers by Polanyi, M., Zeitschr. f. Physik, 1, p. 337 (1920), 2, p. 90 (1920), 3, p. 31 (1920).CrossRefGoogle Scholar

* Equations marked * are equations so numbered in Lewis and Smith's paper.Google Scholar

† Comp. Marcelin, R., Annales de Physique, 3 [9], p. 120 (1915);CrossRefGoogle ScholarTolman, R. C., Journ. Amer. Chem. Soc. 42, p. 2506 (1920). AlsoCrossRefGoogle ScholarChristiansen, J. A., Reaktions-kinetiske Studier, Köbenhavn, 1921. (Dissertation.)Google Scholar

‡ In this connection attention should be drawn once more to the paper of Scheffer, F. E. C., Proc. Akad. Wet. Amsterdam, 19, p. 636 (1917)Google Scholar, where it is proved that the integrated form of equation (1),

must in all simpler oases correspond so nearly to the experimental values, that only by means of very exact experiments will it be possible to measure the deviations.

* This question is not to be discussed here, but must be emphasized that Messrs Lewis and Smith are, in the paper considered, working on an assumption which is very similar to, although not exactly the same, as the above. Compare their equation (3) and the remark, p. 1514: “The work of Arrhenius….” The difference is, that we have replaced the right-hand side of (3),Google Scholar

, by a summation (or integration), as we assume that the reacting molecules are not all in exactly the same state. This extension seems to us to be very natural and even necessary. It may also be emphasized here that equation (2) does not tell anything of the conditions for reaction. It simply states that if the velocity constant varies with temperature there must be a difference between the mean energy of the reacting molecules and the total mean energy.

‡ This is the point, mentioned before, which will be dealt with later on.Google Scholar

† Comp. Christiansen, , Zeitschr. Physik. Chem. 103, p. 92 (1922)Google Scholar and Kramers and Christiansen, ibid. 104, p. 451 (1923).

* See for example the phrase in italics between (24) and (25).Google Scholar

† Warburg, and Leithauser, , Ann. der Physik, 28, p. 313 (1909).CrossRefGoogle Scholar

‡ loc. cit. 3, p. 34 (1920).Google Scholar

* For literature the reader is referred to Journ. Phys. Chem. 28, p. 145 (1924).Google Scholar

* In recent years C. N. Hinshelwoods' measurements of velocities ot gas-reactions have contributed much to the experimental verification of equation (4).Google Scholar

* Phil. Mag. 47, p. 257 (1924).CrossRefGoogle Scholar

† A closer examination of these expressions shows that A 1 and A 2 are very closely connected with the activities of the molecules (1)and (2) respectively, and consequentlyGoogle Scholar

with the activity coefficients.

* See p. 443.Google Scholar

* This equation shows that E* in the case considered by Lewis, and Smith, , loc. cit. p. 1519, is not 24,700 cals. (= Q) but Q + 6RT=28,300 cals., so that their P* should not be 300 but this number multiplied by e−6 = 1/400.Google Scholar

* Zeit. f. Phys. 3, p. 31 (1920).CrossRefGoogle Scholar